1. Field of the Invention
The present invention relates generally to chemiluminescence detection and more specifically to the chemiluminescence detection of gaseous analytes.
2. Description of the Background Art
Various chemiluminescence schemes have been successfully applied to the detection of metals, polycyclic aromatic hydrocarbons, and numerous oxidizing and reducing agents. These methods typically rely upon the oxidation of a chemically reactive species, e.g. luminol or lucigenin, by the analyte of interest, and the subsequent emission of a photon from an electronic, excited-state intermediate. Chemiluminescence techniques are free of Raman and Rayleigh scattering, interferences associated with fluorescence techniques, and, therefore, permit the operation of a photomultiplier tube at maximum sensitivity. The primary attraction of chemiluminescence detection is the excellent sensitivity obtainable over a wide dynamic range using simple instrumentation.
The vast majority of work done in the chemiluminescence field has been devoted to solution-based, flow injection analysis formats. One of the most widely investigated chemiluminescence reagents is 3-aminophthalhydrazide, or luminol. Luminol has been effectively used for the detection of many different metals and oxidants in solution, due to the catalytic behavior these metals have on the chemiluminescent oxidation of luminol. Examples include the detection of Cr(III), Co(II), Fe(II), H2O2(aq), NO(aq), and ClO-(aq). These methods require adequate mixing of the reagent and unknown solutions prior to passage before a photomultiplier tube (PMT), accurate control of the solution delivery to the PMT, and the consumption of a substantial amount of reagents.
Different instrumental variations, based upon the chemiluminescent oxidation of luminol, have been devised for the detection of gas-phase oxidants. Maeda et al., Anal. Chem., 1980, 52, 307-311, designed a chemiluminescent reaction compartment for the detection of NO2(g) which collected a pool of alkaline, luminol solution directly below a PMT, and introduced the sampled air stream into the region above the solution. Excess luminol solution and air flowed continuously out of the reaction compartment through an outlet port at the base of the system. This system was very sensitive to movements of the compartment, and had a relatively slow time response.
An alternate design for the chemiluminescent detection of NO2(g) was subsequently presented by Wendel et al., Anal. Chem., 1983, 55, 937-940, wherein a length of filter paper was positioned adjacent to a PMT, and a flow of alkaline, luminol solution was directed down the paper in a fine film. This system has also been used for the measurement of trace levels of ambient ozone, utilizing the chemiluminescent dye, eosin Y. Anal. Chem., 1986, 58, 598-600. A further variation on the instrument described by Wendel et al. led to the development of a commercially available instrument devoted to the measurement of NO2(g), the Luminox(copyright) LMA-3 (Scintrex/Unisearch); a detailed description of this instrument was presented by Schiff et al. Water Air Soil Pollut., 1986, 30, 105-114. The reaction cell consists of a fabric wick positioned in front of a PMT that is continually wetted with fresh luminol solution delivered via a peristaltic pump, and whose surface is exposed to a stream of the ambient air pumped through the cell. In recent years, this instrument has been utilized in combination with various pretreatment stages for the trace detection of organic nitrates. Blanchard et al., Anal. Chem., 1993, 65, 2472-2477; Hao et al., Anal. Chem., 1994, 66, 3737-3743. Still another variation on the luminol chemiluminescent detector for NO2(g) was introduced by Mik{haeck over (u)}ska et al., Anal. Chem., 1992, 64, 2187-2191; this configuration employs a continuous spray of luminol solution, directed immediately below the PMT, and generated from a stream of the analyzed gas.
Each of the systems referenced above requires accurate and continual pumping or delivery (e.g. peristaltic pump) of an aqueous luminol solution, be it across a piece of filter paper, a wick, or mixed with an additional solution and/or gas containing the analyte of interest. The systems described above are not amenable to remote sensing or personal dosimeter applications because of constraints with respect to size, weight, power, or portability.
The industrial community is continually striving to develop sensor systems which are simpler, less expensive, more compact, and offer the possibility for remote sensing or personal dosimeter applications. In order to address some of these constraints, efforts have been made to develop a solid-phase, chemiluminescent, chemical sensor.
Previous authors have demonstrated the feasibility of utilizing luminol in a reagent-less fashion, i.e. using a solid substrate support. Agranov and Reiman attempted the direct application of luminol, sodium carbonate, and copper sulfate onto indicator tape for the detection of hydrogen peroxide, but were plagued by humidity and stability problems. Agranov et al., Zh. Anal. Khim., 1979, 34, 1533-1538. Freeman and Seitz determined hydrogen peroxide concentrations in solution by immobilizing luminol and peroxidase within a polyacrylamide gel held on the end of a fiber optic probe. Freeman et al., Anal. Chem., 1978, 50, 1242-1246. The co-immobilization of dehydrogenase enzymes and luminol within a polyvinyl alcohol matrix has been proposed for the detection of ATP or NAD(P)H. Coulet, et al., Sensors and Actuators B, 1993, 11, 57-61. Luminol has also been covalently immobilized onto silica particles for the detection of hydrogen peroxide by flow injection analysis. Hool et al., Anal. Chem., 1988, 60, 834-837.
Generally, the analytical use of chemiluminescence requires selectivity for the analyte. In most, but not all, chemiluminescent systems, this need for selectivity presents problems.
Accordingly, it is an object of this invention to detect a gaseous material with a solid-phase chemiluminescent sensor.
It is another object of the present invention to provide a small, portable chemiluminescent sensor for the detection of gaseous analytes.
It is a further object of the present invention to vary the sensitivity of a solid-phase chemiluminescent sensor to favor the detection of a selected gaseous analyte in a mixture of gaseous materials.
These and additional objects of the invention are accomplished by a solid phase chemical sensor including a polymeric film which has immobilized therein a chemiluminescent reagent, a catalyst, if desired, and a buffer, if desired. The polymeric film and chemiluminescent reagent are chosen to significantly enhance the selectivity of the sensor to the analyte in the gaseous phase to which the sensor is exposed. Similarly, any catalyst or buffer used are also selected to significantly enhance the selectivity of the sensor to the analyte in the gaseous phase to which the sensor is exposed. The sensor is then positioned so that, when exposed to the gaseous mixture, any chemiluminescence generated will be detected by a photomultiplier tube or other photoelectric device, such as a photodiode.